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Results of warm-up and fuel economy studies on a dual catalyst system using GEM reinforced Ni-Cu NOx reduction catalysts and PTX®-II B oxidation catalysts are reported. Rapid warm-up of this system is required to control emissions to the target level of 3.4 g/mi. CO, 0.41 g/mi. HC, and 0.4 g/mi. NOx. This rapid warm-up can be obtained only by oxidizing the CO, HC, and H2 in the exhaust during the first 30-60 seconds after start-up. Methods of inducing oxidation are described. Controlling NOx to 0.4 g/mi. requires GEM catalyst temperatures of ∼1300°F., 2-300°F. hotter than exhaust temperature during warmed-up operation. The additional temperature can be generated by enriching carburetion and oxidizing the CO, H2, and HC formed, or by spark retard. Studies conducted on a 1973-350 CID Chevrolet indicate a ∼4%/100°F. fuel penalty for increasing temperature by richer carburetion and air bleed at constant spark timing, and a ∼8%/100°F. penalty for spark retard at constant carburetion.